Soil organic matter levels appear to equilibrate under Canadian conditions at approximately 75% in the 4 to 5% level typical of a cereal grain-hay rotation(Rennie 1979). In Indiana, Barber(1979) found that organic matter decreased to 90% of the original level after ten years; in Iowa Larson et al.(1972) found that organic matter decreased to 87% of the initial level after twelve when years all surface residues were removed. The decline inorganic matter is slow, but it is also a slow process to increase it.